P885: SOLITARY PLASMACYTOMA: SINGLE INSTITUTION EXPERIENCE AND SYSTEMATIC REVIEW AND META-ANALYSIS OF CLINICAL OUTCOMES
Authors: Charalampos Charalampous, Jean-Sebastien Claveau, Prashant Kapoor, Moritz Binder, Francis Buadi, Joselle Cook, David Dingli, Angela Dispenzieri, Amie Fonder, Morie Gertz, Wilson Gonsalves, Suzanne Hayman, Miriam Hobbs, Yi Hwa, Taxiarchis Kourelis, Martha Lacy, Nelson Leung, Yi Lin, Rahma Warsame, Robert Kyle, Vincent Rajkumar, Shaji Kumar
Journal: HemaSphere (2023)

Topic: 14. Myeloma and other monoclonal gammopathies - Clinical Background: Solitary plasmacytomas are rare plasma cell neoplasms located in bone or extramedullary sites. Information on risk factors affecting disease-free survival (DFS) and survival outcomes is lacking. Aims: To report the DFS of a large cohort of plasmacytoma patients and establish risk factors for earlier progression. Methods: We conducted a retrospective study on 147 patients with plasmacytoma seen at the Mayo Clinic (January 1st, 2005 – June 30th, 2022). Our primary outcome was DFS, measured from the date of diagnosis to plasmacytoma recurrence or progression to multiple myeloma. We also performed a systematic review (1960 - 2022) and meta-analysis of 62 studies and 3487 patients with solitary plasmacytomas. Forest plots were constructed for each meta-analysis to examine and display study-level data using the random-effects model. Results: The median age at diagnosis was 60.7 years (range: 15.4 - 83.6). Patients with up to 10% clonal plasma cells in the bone marrow (plasmacytoma +, N=72) were older than those with a true solitary (N=75) plasmacytoma (63.5 vs. 56.2 years, p<0.05). The plasmacytoma + patients had significantly shorter median DFS (15.7 vs. 79 months, p<0.05) than those with true solitary plasmacytoma. The 3, 5, and 10-year DFS rates were 31%, 20%, and 6% for patients with plasmacytoma + and 64%, 53%, and 40% for patients with solitary plasmacytoma, respectively. In univariate analysis, clonal plasma cells in the marrow were a significant risk factor for a shorter time to progression (HR= 2.9). In subgroup analysis for patients with plasmacytoma +, a DFLC> 5 mg/dl (HR= 1.9) and a positive urine immunofixation (HR= 3.4) were the only significant risk factors for earlier progression. In contrast, for solitary plasmacytoma, only a DFLC>5 mg/dl (HR= 2.7) retained significance. In the meta-analysis, most patients were male (66.1%) with a median age of 58 years and a tumor size of 4.9 cm. Radiation therapy was the main treatment, with 90.6% receiving it alone or in combination with other therapies. The objective response rate was 92.6%, with a 3-year DFS rate of 66.9%, 5-year DFS of 55%, and 10-year DFS of 42.1%. The 5-year overall survival (OS) rate was 79.6%, and the 10-year OS rate was 64.7%. There was a significant difference in the 5-year DFS rate between patients with bone plasmacytomas (51.1%) and extramedullary locations (69.8%), p<0.01. The OS was numerically shorter in patients with bone plasmacytoma than with extramedullary plasmacytoma, respectively (76.7% vs. 81% at 5 years and 61% vs. 70.1% at 10 years, p=NS). Summary/Conclusion: The study provides important insight into survival outcomes and risk factors for plasmacytoma patients and highlights the importance of comprehensive disease staging at diagnosis.Figure 1. Disease-free survival (DFS) in patients with plasmacytoma (+) vs. true solitary plasmacytoma in the Mayo cohort. Keywords: Multiple myeloma, Bone disease, Progression